PERIPHERAL THERMAL THRESHOLDS AND THERMOEFFECTORS THRESHOLD ZONE IN MALAYSIAN AND JAPANESE MALES Joo-Young Lee1), Mohamed Saat2), Chin-Mei Chou3), Titis Wijayanto1), Hitoshi Wakabayashi1),Yutaka Tochihara1) 1)
Department of Ergonomics, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan 2) School of Health Sciences, Universiti Sains Malaysia, Malaysia 3) Industrial Technology Research Institute, Technology Center for Service Industries, Taiwan
Joo-Young LEE:
[email protected] INTRODUCTION Heat acclimatization is triggered as a response to a complex of environmental factors in hot climate. A number of studies on heat acclimatization have been reported in terms of physiological adaptation (such as body temperature and sweating responses) (Saat et al., 2005; Saat & Tochihara, 2008), while studies on heat acclimatization in cutaneous thermal sensitivity are relatively rare. It is known that long term changes in a thermal environment can reach the central nervous system either directly, by deviation of core temperature, or indirectly, via thermoreceptors (Hensel, 1982). Cutaneous thermal receptors transmit information about the temperature of the external surface of the body (Iggo, 1970), and mediate the autonomic temperature regulation, and the experiences of thermal comfort and discomfort (Hammel,1968; Hardy, 1961; Hensel, 1982; Nadel et al., 1973). These experiences motivate our thermoregulatory behaviour. The purpose of this study was to investigate: 1) differences in cutaneous warm and cool sensations between Malaysian and Japanese males; 2) peripheral thermoeffector zone estimated from an inter-threshold zone between cool and warm sensations in two ethnic groups.
METHODS Ten Malaysians (MY) and ten Japanese (JP) young males participated in this study (JP: 21±1yr in age, 168.9±4.5cm in height, 62.6±5.3kg in weight, 1.75±0.09m2 in BSA, 14.1±2.8%bodyfat, 41.8±4.8ml·min-1·kg-1 in VO2max, 24.2±4.7g·hr-1·m-2 in insensible body mass loss, 0.77±0.05kcal·min-1·m-2 in resting metabolism; MY: 22±2yrs, 167.9±5.4cm, 65.2±11.1kg, 1.77±0.15m2, 19.0±5.7%BF, 39.6±3.6ml·min-1·kg-1,24.1±4.3g·hr-1·m-2,0.82±0.11kcal·min-1·m-2). Ten Malaysian males were invited from Malaysia to Fukuoka, Japan to participate in the present study as volunteers. Each subject stayed in Fukuoka for two weeks for the participation. Peripheral warm and cool thresholds were measured on 12 body regions (the forehead-FH, chest-CH, abdomen-AB, back neck-NK, upper back-BK, forearm-FA, hand-HD, palm-PM, thigh-TH, calf-CF, instep-IT, and sole-SL on the left side of the body), using a stimulator with a thermo-electronic probe and a push-button switch (Intercross-200, Intercross, Japan). The surface area of the probe in contact with the skin was 25×25mm (6.25cm2). The speed of
warming and cooling of the probe was set at 0.1oC·sec-1. All subjects were instructed to push the timer-switch the moment they felt a ‘slightly warm’ or ‘slightly cool’ sensation from their thermal neutral state. The surface temperature, the change of surface temperature, heat flux on/through the surface of the probe, etc. were simultaneously recorded. Skin temperatures (Tsk) were recorded every second on the adjacent 12 body regions of the thresholds measurement body sites (LT-8A, Gram Ltd, Japan). Mean skin temperature (mean Tsk) was estimated from a modified Hardy-DuBois’ equation. Rectal temperature (Tre) was monitored at a depth of 13cm from the anal sphincter every second (LT-8A, Gram Ltd, Japan). Subjects had laid supine on a bed for at least two hours. Insensible body mass loss was estimated by the difference between body mass before and after the experiment. Resting energy metabolism (Mrest) and VO2max were measured on different days. The climatic chamber was maintained at an air temperature of 28 oC with 50%RH. Each subject wore only shorts. Body hairs on the calf and thigh were shaved beforehand, as large as 4×4cm each. Subjects had laid supine on a portable net bed equipped in the climatic chamber. After 30min-stabilization on the net bed, thermal threshold measurement was conducted. All measurements were repeated three times and were done between 14:0018:00PM. Before measuring, careful instructions were provided in the subject’s own language and all subjects were pre-adapted to thermal threshold measurements. Throughout the present study, the detectable temperature range (DTR) was defined as the rise/fall of skin temperature once the subject initially detects a warm/cool sensation during the warming/cooling of the body skin, starting from thermal neutral state of the skin. Interthreshold’s zone was defined as the distance of DTR between a ‘slightly warm’ and ‘slightly cool’ sensation. Peripheral thermoeffector threshold zone (PTTZ) represents the inter-threshold’s zone as a sum of DTR to warmth and coolness. Weighted means of Tsk at the warm/cool thresholds, DTR on 12 regions, and PTTZ were calculated with the same coefficients of Hardy & DuBois’ 7-point mean-Tsk equation:Weighted mean PTTZ=0.07(PTTZforehead+PTTZneck)/2 + 0.35(PTTZchest+PTTZabdomen+PTTZupper back)/3 + 0.14(PTTZupper arm+PTTZforearm)/2 + 0.05PTTZhand + 0.19PTTZthigh + 0.13PTTZcalf + 0.07PTTZfoot. A regional sensitivity coefficient was defined as a ratio
of thermal sensitivity normalized by the baseline calf sensitivity coefficients, in terms of detectable temperature range. The value was calculated in the following manner (e.g., Warm insensitivity coefficient of the forehead = Detectable temperature of the forehead/Detectable temperature range of the calf; Warm sensitivity coefficient = Warm insensitivity coefficient-1). ANOVA was conducted to test the differences by two ethnic groups and 12 body regions. Duncan’s Post-hoc test was carried out on the items that showed significant differences in body regions after ANOVA. A significance was set at p
